Short-term use of left ventricular assist devices (LVADs) has been shown to reverse the effects of congestive heart failure, a devastating condition that will ultimately afflict one in every five Americans. When used for permanent support however, LVAD therapy has been limited by serious complications caused by percutaneous drivelines and blood contacting surfaces. Here we propose to assemble and test a non-blood-contacting muscle-powered LVAD system that avoids the limitations of current heart assist devices and so could potentially represent a major advance in the treatment of congestive heart failure. As a first step toward this goal, we have developed an implantable muscle energy converter (MEC) capable of transforming contractile energy into hydraulic power. The objective of this project is to assemble and test a non-blood- contacting ventricular assist system powered by this device. The central hypothesis to be tested is that the mechanical power of conditioned skeletal muscle can be converted into hydraulic energy by the MEC and used to drive a permanent cardiac assist device. The rationale behind the proposed research centers on the fact that skeletal muscles express oxidative (fatigue-resistant) phenotypes in response to chronic activation and that trained latissimus dorsi (LD) muscles have been shown to perform work at rates compatible with long- term cardiac assistance. Thus, given the limitations of current medical therapies for congestive heart failure, the difficulties associated with delivering extracorporeal power to aid the failing heart, and the serious complications cause by blood contacting surfaces, research to develop and test a non-blood-contacting muscle-powered blood pump is warranted. To accomplish the objectives of this research, the following three specific aims are proposed: 1) Build mVAD prototype devices and test on the bench to document functional parameters and assess long- term mechanical reliability; 2) Implant prototype mVAD systems (acute experiments) to refine implantation methods, evaluate anatomic fit, and document acute biological reactions at the tissue/device interface; and 3) Perform short-term (28-day) implant studies in animals with heart failure to establish in vivo system functionality, document chronic biological reactions at the tissue/device interface, quantify hemodynamic effects, and determine the overall efficacy of the mVAD system. Our expectations are that, at the conclusion of the proposed period of support, we will have demonstrated the viability of harnessing energy from in situ muscle for long-term circulatory support. We further expect that practical application of this technology will have been demonstrated via in vivo evaluation of a complete muscle-actuated ventricular assist system.